Java中的 ByteBuffer mark() 方法及示例

Java.nio.ByteBuffer 类的mark()方法用于设置这个缓冲区的标记在它的位置。

句法：

public ByteBuffer mark()

返回值：此方法返回此缓冲区。

以下是说明 mark() 方法的示例：

示例 1：

// Java program to demonstrate
// mark() method
  
import java.nio.*;
import java.util.*;
  
public class GFG {
  
    public static void main(String[] args)
    {
  
        try {
  
            byte[] barr = { 10, 20, 30, 40 };
  
            // creating object of ByteBuffer
            // and allocating size capacity
            ByteBuffer bb = ByteBuffer.wrap(barr);
  
            // try to set the position at index 2
            bb.position(2);
  
            // Set this buffer mark position
            // using mark() method
            bb.mark();
  
            // try to set the position at index 4
            bb.position(4);
  
            // display position
            System.out.println("position before reset: "
                               + bb.position());
  
            // try to call reset() to restore
            // to the position we marked
            bb.reset();
  
            // display position
            System.out.println("position after reset: "
                               + bb.position());
        }
  
        catch (InvalidMarkException e) {
            System.out.println("new position is less than "
                               + "the position we marked before ");
            System.out.println("Exception throws: " + e);
        }
    }
}

输出：

position before reset: 4
position after reset: 2

示例 2：演示 InvalidMarkException

// Java program to demonstrate
// mark() method
  
import java.nio.*;
import java.util.*;
  
public class GFG {
  
    public static void main(String[] args)
    {
  
        try {
  
            byte[] barr = { 10, 20, 30, 40 };
  
            // creating object of ByteBuffer
            // and allocating size capacity
            ByteBuffer bb = ByteBuffer.wrap(barr);
  
            // try to set the position at index 2
            bb.position(2);
  
            // Set this buffer mark position
            // using mark() method
            bb.mark();
  
            // try to set the position at index 4
            bb.position(1);
  
            // display position
            System.out.println("position before reset: "
                               + bb.position());
  
            // try to call reset() to restore
            // to the position we marked
            bb.reset();
  
            // display position
            System.out.println("position after reset: "
                               + bb.position());
        }
  
        catch (InvalidMarkException e) {
            System.out.println("\nnew position is less than "
                               + "the position we marked before ");
            System.out.println("Exception throws: " + e);
        }
    }
}

输出：

position before reset: 1

new position is less than the position we marked before 
Exception throws: java.nio.InvalidMarkException

参考： https://docs.oracle.com/javase/9/docs/api/ Java/nio/ByteBuffer.html#mark–